The present invention relates to a drive speed control system for controlling the transmission ratio and a constant speed drive for a motor vehicle, and more particularly to a system for accelerating the vehicle during the constant speed drive.
In a control system for a constant speed drive (hereinafter called a cruise control system) for a motor vehicle having an automatic transmission, when the acceleration of the vehicle is selected by the driver, the vehicle is accelerated by increasing the opening degree of a throttle valve without downshifting the transmission.
Japanese Patent Application Laid-Open 60-135335 discloses a cruise control system for a motor vehicle with a continuously variable belt-drive automatic transmission (CVT) wherein a current control means is provided for controlling current passing to a vacuum operated throttle actuator in accordance with the difference between a set vehicle speed Vs and an actual vehicle speed V. A correcting means is provided for correcting transmission ratio i for the transmission in accordance with current or a control signal for the current control means, thereby controlling the actual vehicle speed V to the set vehicle speed Vs.
However, the acceleration of the vehicle depends solely on the increasing rate of the engine torque. Thus, the vehicle is slowly accelerated.